Tropical Storm Leslie Forecast Discussion

000
WTNT43 KNHC 111448
TCDAT3

Tropical Storm Leslie Discussion Number  37
NWS National Hurricane Center Miami FL       AL132024
1100 AM AST Fri Oct 11 2024

Leslie remains a sheared tropical storm.  The low-level center is 
exposed about 70 n mi outside of the northern edge of the convective 
area, which has been shrinking and weakening over the past several 
hours.  As a result, subjective Dvorak estimates from TAFB and SAB 
are both down to 45 kt.  A pair of recently arriving ASCAT passes 
still show an area of 40-44 kt winds in the eastern semicircle.  The 
initial intensity is set to 45 kt, which agrees well with the 
subjective Dvorak estimates and the ASCAT data.

Leslie is likely currently experiencing more than 30 kt of 
north-northeasterly vertical wind shear.  The cyclone will be moving 
toward an upper-level ridge axis over the next 12 to 24 h, which 
will cause the deep-layer shear to decrease.  However, Leslie will 
reach sea-surface temperatures colder than 26C in about 24 h, and it 
is forecast to remain in a relatively dry low- to mid-level 
troposphere.  Some slight additional weakening is forecast today, 
followed by little change in strength for the next couple of days. 
The intensity forecast is near the middle of the intensity model 
guidance envelope.  The GFS and ECMWF simulated satellite imagery 
agree that the cyclone will lose its convection by 48 h, but 
phase-space diagrams suggest that Leslie could potentially become 
extratropical before that time, by 36 h.  The NHC forecast continues 
to show Leslie becoming post-tropical over the weekend, in agreement 
with the aforementioned guidance.  Leslie is still expected to 
dissipate by day 4, as shown by the global models.

Leslie has been moving toward the north-northeast, or 015/9 kt, as 
the cyclone rounds the western periphery of a subtropical ridge.  A 
strong frontal trough will approach Leslie from the west tonight 
into Saturday, causing Leslie to accelerate toward the northeast. 
Leslie's interaction with this frontal system could cause the 
cyclone to lose its tropical characteristics by Saturday night.  On 
Sunday, the cyclone is expected to turn more towards the east within 
the mid-latitude westerly flow.  No significant changes were made to 
the first 48 h of the official track forecast, with a slight 
southward adjustment at the 72 h point.  The NHC track forecast is 
very near the TVCA consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 26.4N  50.5W   45 KT  50 MPH
 12H  12/0000Z 28.4N  48.9W   40 KT  45 MPH
 24H  12/1200Z 31.7N  45.1W   40 KT  45 MPH
 36H  13/0000Z 34.6N  39.9W   40 KT  45 MPH...POST-TROPICAL
 48H  13/1200Z 36.2N  34.4W   40 KT  45 MPH...POST-TROPICAL
 60H  14/0000Z 36.8N  29.3W   35 KT  40 MPH...POST-TROPICAL
 72H  14/1200Z 36.4N  24.6W   30 KT  35 MPH...POST-TROPICAL
 96H  15/1200Z...DISSIPATED

$$
Forecaster Hagen